Inorganic boron compounds are well established as preservatives for timber and other materials against attack from fungi or insects. Recent developments have included the use of shaped rods, pellets or tablets of inorganic boron compounds for insertion into pre-formed cavities in timber. U.S. Pat. No. 4,269,875 describes shaped timber preservative elements comprising fused monolithic bodies of wood preservative containing boron compounds, particularly boric oxide. These elements are most suitable in the treatment of timber such as new joinery, prior to fungal attack as a protective rather than remedial treatment, as they are only slowly soluble and have extensive lives in situ. A disadvantage of these elements is that they are expensive as they are difficult to manufacture except by casting.
U.K. Patent 2,114,003 proposes preservative tablets of inorganic boron compounds which are shaped by compression to fit in pre-formed cavities in timber or other materials. These tablets dissolve more rapidly than the fused products of U.S. Pat. No. 4,269,875 in the moisture contained in the timber but suffer from the disadvantage of being mechanically weak except when prepared in the presence of a suitable adhesive binder such as starch.
Both the tablets and fused elements rely solely upon the moisture present in the location in which they are inserted within the timber to dissolve the preservative and transport it through the grain to the areas to be protected. Under some conditions this may lead to too little preservative being transported in time to prevent the onset of decay. This difficulty has been recognized and the use of highly concentrated solutions of inorganic borates and boric acid in glycols has been proposed to be used in conjunction with fused borate elements or borate tablets to overcome the problem. According to U.S. Pat. No. 4,610,881, the glycol assists the borate in penetrating the outer parts of the wood more rapidly.
Other shaped bodies of inorganic borates capable of binding water by hydration, and their use as preservatives, are described in U.S. Pat. No. 4,661,157.